Considerable attention in recent years has been directed to the intravenous delivery of fluids such as saline solutions and the like to patients. Initially, these fluids were administered to the patient by means of gravity flow from a container holding the fluid to be delivered. Gravity-flow devices, however, can be cumbersome to use, inasmuch as pressure sufficient to sustain fluid movement in a gravity-flow device often required positioning of the device at a considerable elevation above the patient receiving the fluid. Moreover, attempts to accurately regulate the amount of fluid administered by gravity-flow devices were often unsuccessful because of the fact that the gravity-induced pressure responsible for moving fluid through the device generally decreased during the intravenous delivery operation as the fluid level within the container holding the fluid dropped.
In order to provide for improved flow of fluids to patients, pumping devices have been utilized, such as found in U.S. Pat. Nos. 4,336,800; 4,453,931; 4,453,932; and 4,457,713. Such pumping devices employ a metering device control unit into which an intravenous metering device is placed. The intravenous metering device includes a pumping chamber which includes a reciprocal diaphragm. The metering device includes a pumping piston which reciprocates the diaphragm thereby changing the volume of the pumping chamber. Check valves are positioned at the pumping chamber inlet and outlet to regulate the flow of fluid and a gas retention chamber is provided upstream of the pumping chamber and the pumping chamber inlet. The gas retention chamber is connected via tubing to a fluid source while the pumping chamber outlet is connected to a patient.
The intravenous metering devices found in these patents all employ complex structure including a biased ball check valve. While such check valve performs adequately, the multiplicity of moving parts is undesirable due to cost factors and the variation in functionality associated with manufacturing complexity. What is thus needed is an intravenous metering device which improves on the use of such biased ball check valve.